Impact of Dynamic Scatterers upon Frequency- and Amplitude-Modulation

Björn Neubauer

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In 1959 Anderson et. al publish their paper „The CAA Doppler Omnirange”. In that contribution they present their an...

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In 1959 Anderson et. al publish their paper „The CAA Doppler Omnirange”. In that contribution they present their analytically derived receiver‑model for quantifying the bearing error of the Doppler VOR (DVOR) due to multipath propagation. At that time this model exclusively serves for comparing the susceptibility of the DVOR with the one of its precursor which is the conventional VOR. For this purpose, they take the impact of a static omnidirectional scatterer solely upon one signal component into account, which is the frequency modulated one. Due to the number of already installed wind turbines and especially due to the desire to install way more turbines, the signal integrity of the DVOR has become a very timely topic in Germany in the context of renewables energies. In this dissertation Anderson’s basic generic model is both improved and substantially extended with respect to the impact of wind turbines upon the multipath signal.  In the first part of this work Anderson’s error model is quantitively expended with respect to the relative amplitude of the scattering path. Furthermore, the analytical model is fundamentally improved with respect to quality: For the first time the analytical model allows to take the dynamic effects of wind turbines into account, i.e. both Doppler shifts as well as an additional amplitude modulation due to the scattering object — namely the wind turbine. Additionally, this analysis is carried out for the DVOR’s reference provided by an amplitude modulated signal component, which has been completely neglected so far by the current state of the art. These analytical models allow for extensive parameter studies, which are applicable e.g. for the validation of both numerical simulation tools as well as approaches by measurements. In the second part of this work the dynamic impact of wind turbines upon the DVOR’s bearing intelligence is investigated by measurements. This is carried out in an environment scaled with a ratio of 1:144. It utilizes the equipment realized within the projects “Sk-ILS” and “min-Vor-Win” and expands it by inventing a procedure for crafting and electromagnetically characterizing voluminous scattering bodies. These allow for a systematic analysis of the impact of terrain topologies. A variety of measurements and the corresponding fundamental analysis address: Doppler shifts and Doppler spectra depending on the orientation of the plane of rotation, the blades’ shape, revolutions per minute, and the position of the turbines as well as the amplitude and width of Doppler spectra. Fundamental results of this work are e.g.: A 10 km safety‑radius of the DVOR’s protective area, up to now applied in Germany and as well recommended by the ICAO, can be considered way to restrictive. Furthermore, the receiver settings play a crucial role, when determining the bearing error. Thus, stating the latter makes it mandatory to state the receiver settings as well.